1. Field of the Invention
The invention relates, generally, to pneumatic valve assemblies and, more specifically, to a poppet valve having an improved valve seat.
2. Description of the Related Art
Pneumatic valve assemblies are well known in the art for controlling the flow of pressurized air to and from various pneumatically actuated devices such as linear actuators, rotary actuators, air outlets or any other pneumatic device or application requiring precise control of operating air. One type of pneumatic valve currently employed in numerous applications in the related art is generally known as a poppet valve. Poppet valves find particular use, for example, in connection with pilot operated pneumatic valves as a part of an overall fluid powered system. One common poppet valve arrangement includes a valve member movably supported within a valve body between predetermined positions. These positions are typically defined by the placement of the valve seats within the valve bore. The valve member has valve elements that engage the seats. The valve member is moved between the predetermined positions by one or more actuators. Typically, at least one of the actuators includes an electromechanical device, such as a solenoid, that moves the valve member in one direction. The poppet valve assembly may include a biasing member, such as a coiled spring, or even another electromechanical actuating device that moves the valve member in the opposite direction. In this way, the flow of pneumatic pressure within the valve is controlled between various ports formed in the valve body.
Depending on how the valve body is configured internally, the valve may be constructed in either a xe2x80x9cnormally openxe2x80x9d or a xe2x80x9cnormally closedxe2x80x9d configuration, in reference to the initial state of the flow passage from the inlet port to the outlet port of the valve assembly. Additionally, there are known valve assemblies having two, three, or four-way valve flow paths, which can provide multiple internal pneumatic flow paths between a number of inlet and outlet ports. This allows the valve body to be configured to provide some ports as xe2x80x9cnormally openxe2x80x9d and some as xe2x80x9cnormally closedxe2x80x9d, depending on the application. Thus, the two, three, or four-way valve assemblies can concomitantly open and close a number of inlet and outlet ports when activating the valve member.
Valve assemblies of this type are employed in a wide variety of manufacturing and process environments where repeatable and very fast response times are desired. More specifically, as noted above, poppet valves currently known in the related art may be used to pilot or control the flow of pneumatic pressure within a main spool valve. However, those having ordinary skill in the art will appreciate from the description that follows that the present invention is not limited in any way to its use as a pilot valve.
In any event, as the technology for these valves has advanced, there has been an increase in the demand for physically smaller valves, which are desired for their ability to be placed in ever tightening work spaces, closer and closer to the active pneumatic devices. Over the years, there have been a number of improvements in this field, which have facilitated high flow rates and repeatable, fast response times in relatively small valves. Yet, as faster and smaller valves have evolved, certain limitations and drawbacks of conventional valve assemblies relating to life cycle durability, repeatability, and valve accuracy have become apparent. Certain high-speed manufacturing and process environments perform repetitive pneumatically driven operations in extremely high numbers over a relatively short period of time. For example, over the course of a year, many of the above-mentioned applications require that these types of pneumatic valves perform literally billions of repetitive actuations while maintaining their original accuracy and sealing properties.
Typical valve assemblies currently employed in the related art are subject to wear and durability limitations and display distinct disadvantages when used in rigorous environments that require high-speed, and high-repetition valve operation. One important factor for maintaining valve assembly operating performance while providing high numbers of repetitive valve actuations lies in maintaining an accurate and consistent valve stroke within the valve body. Any increase in stroke will alter the timing of the valve actuation and increases detrimental internal forces.
One consideration to maintaining a consistent stroke and thereby valve longevity is the nature of the valve seat and valve member interaction. Valve seats commonly employed in the related art typically include a square cut or 90xc2x0 corner surface. The corresponding valve element usually includes a relatively conical or angularly-formed valve sealing surface. Most often, the valve element is over-molded, or encapsulated, with a resilient material to improve the sealing effect and provide a slight cushioning of the valve member as it interacts with the squared valve seat. The square cut 90xc2x0 corner of the valve seat can penetrate deep into the poppet valve element during valve operation. As it penetrates, the force being applied to the valve element is spread out across the valve-sealing surface. This sealing interaction initially tends to create a good seal as the over-molded material on the sealing surface of the valve element deflects inwardly slightly as it rests against the edge of the seat thereby creating a ring seal about the seat. However, this sealing effect creates wear as the valve is repetitively activated by causing the sealing material to be repetitively deformed and ultimately damaged, for example by being cut as the valve member moves to its seated position against the valve seat during each and every valve closing event.
As the sealing material begins to permanently deform and then finally cut, the actuator must make a longer and longer stroke to seal the valve. This minimal, yet critical, on going lengthening of the valve stroke introduces a dynamic change to the timing of the valve actuation, which degrades the operation being performed. Changes in the timing of the valve actuation due to changes in the valve stroke translates into process inaccuracies and inconsistencies that ultimately require valve replacement. Secondly, the deforming and cutting of the valve sealing material may cause leakage and often introduces pieces of the sealing material into the downstream pneumatic flow path.
An additional disadvantage to conventional valves becomes evident when analyzing the actuator structure of the typical valve assembly. Typical electromechanical actuated valve assemblies include solenoids that utilize a floating, or moveable armature. A slight gap is required between the armature and the pole piece. This allows the armature to slideably move, or float, within the actuator while moving the valve member. An armature biasing member, which may sometimes include a lost-motion biasing function, is often employed in this environment. This armature biasing member works in conjunction with the valve biasing member, so that both the valve member and the armature are fully returned to their original positions. This arrangement helps to ensure a consistent stroke length.
The floating armature and lost-motion biasing cause little problem by themselves. However, when the valve stroke length grows due to degradation of the valve seat as described above, the gap built into the actuating assembly cannot accommodate the longer stroke length and the armature will begin to strike the valve body or the pole piece each time the actuator energizes the armature. This causes a xe2x80x9chammer and anvilxe2x80x9d effect between the individual components, damaging them and sometimes hammering off small particles that become introduced into the valve body and the pneumatic flow path. These conditions lead to an increase in rapid valve wear and further shorten the life span of the valve assembly. A shorter life span of the valve assembly results in repeated replacement of these valve assemblies when they are used in high-speed and high-repetition manufacturing and processing environments.
Thus, there remains a need in the art for a pneumatic valve that overcomes these deficiencies and provides the longevity and life cycle accuracy required for use in applications that require a relatively large number of high-speed repetitions. In addition, there remains a need in the art for pneumatic valves that can withstand the rigors of these severe environmental conditions while providing long life, good sealing properties throughout its useful life with consistent accuracy and little or no increase in valve stroke.
The present invention overcomes the disadvantages and drawbacks of the conventional related art by providing a pneumatic valve assembly including a valve body having a pressurized air supply inlet port in fluid communication with a source of pressurized air, a valve bore extending axially within the valve body and a valve member movably supported within the valve bore between predetermined positions to selectively direct a flow of pressurized air from the inlet port through the valve bore to at least one outlet port. The valve assembly further includes an at least one valve element disposed upon the valve member, and having an angular valve sealing surface. At least one valve seat is defined in the valve bore. The valve seat is formed at an angle oblique to the valve bore and adapted to provide a sealing contact with the valve sealing surface of the valve element when the valve member is in a closed position, thereby interrupting the flow of pressurized air.
Due to the angular interaction of the sealing surfaces of the valve elements with the valve seats, the valve seat provides an initial line contact that can become a surface sealing contact that creates the desired seal without having a valve sealing surface that must rest against the edge, or corner, of a square faced valve seat. The angular surface-to-surface seal of the valve seat to the valve element in the present invention minimizes the deflection of the resilient material over-molded on the valve element as it interacts with the valve seat. Therefore, the wear that affects the conventional valve art by the sealing material being repetitively deformed and ultimately cut as the valve member moves to its seated position against the square valve seat during each and every valve closing event is eliminated. This also prevents the undesirable and damaging effects of valve stroke lengthening that occurs in conventional valve assemblies. Therefore, valve timing and accuracy is maintained and the system processes that the valve assembly of the present invention controls remains consistent and reliable. Additionally, valve leakage and particle introduction into the downstream pneumatic flow path caused by the deformation and cutting of the valve sealing material of a conventional valve assembly is also eliminated.